It has been found that the hitherto known bearing unit has a high load carrying capacity against any vertical load as well as lateral thrust load owing to the arrangement of rollers or balls between the bearing unit body and the track shaft or rail at the upper side as well as at both the sides thereof but has a considerably reduced load carrying capacity against an upwardly directed load (floating load).
Further, it has been found that the conventional bearing unit has a reduced mechanical strength due to the fact that longitudinally extending holes are provided through the guide portions of the bearing unit body so that a number of rollers or balls are circulated therethrough.
Since the provision of the longitudinally extending holes through the bearing unit body requires difficult lathing and grinding operations, it represents one of factors which cause the conventional bearing unit to be manufactured at an expensive cost.
To obviate the drawbacks with the conventional bearing unit as described above an improved roller bearing unit with roller guide means incorporated therein for a moving body was proposed which comprises slide ways, guide brackets corresponding to the horizontal portion and inclined portions of said slide ways, said guide brackets being formed with a roller groove respectively, and a preloading mechanism arranged on the guide bracket (c.f. Japanese Utility Model Laid-Open No. 292/1971).
However, it was found that the proposed roller bearing unit has a drawback that sliding frictional resistance becomes increased as rolling friction increases in proportion to increase in applied load, because the rollers located in the non-loading sections are preloaded whereby they are tightly clamped between the retainers and the roller guide means.